Core B: Project Summary The main goal of this program is to conduct a novel analysis of lymphocyte populations in diverse human lymphoid and mucosal tissues in steady state and in organ transplantation, to elucidate mechanisms by which human immune responses are distributed, function and are maintained in the whole body. The proposed studies can uniquely be accomplished by this program through our novel human tissue resource that is the focus of this core. We will use two sources of human samples for the proposed studies in all projects (Projects 1, 2, 3): deceased organ donors and peripheral blood and biopsies from intestinal transplant patients obtained in conjunction with the Columbia Center for Translational Immunology (CCTI) Human studies core. For Service aim 1, we will obtain and process multiple lymphoid and mucosal tissues from human organ donors. We have established the necessary protocols and collaborations with Columbia University Medical Center (CUMC) surgeons and LiveOnNY to obtain from research-consented organ donors, tissues that are not used for life-saving transplantation. We already have the infrastructure set up to obtain multiple primary and secondary lymphoid tissues (bone marrow, thymus, spleen, peripheral, lung- and intestinal draining lymph nodes and tonsils), and mucosal tissues (lungs, small and large intestinal sections) from organ donors whose next-of-kin have consented for the use of tissues for research. The tissues will be processed in the laboratory for obtaining cell suspensions and for preserving tissue sections and cells and/or whole tissues will be distributed to all projects for analysis. For service aim 2, we will coordinate the acquisition of biopsy and peripheral blood samples from transplant patients. In this part of the core, we will obtain biopsy and peripheral blood specimens from intestinal transplant patients who will be enrolled in studies related to Project 3; we will maintain IRB protocols for obtaining samples, enroll patients in this study, and work with the clinicians to obtain biopsy and blood samples, and coordinate storage on unused samples in the CCTI biobank repository. For service aim 3, we will prepare and store tissue sections for imaging by all project laboratories and for a satellite project with Dr. Ron Germain, an intramural investigator at NIAID who will implement his high-dimensional imaging and histocytometry along with advanced computational algorithms to generate an imaging atlas of human immune cells in tissues throughout the body. Together, this core will provide an essential function to this program in the acquisition, processing and distribution of unique human samples to project investigators.